The interaction of enzymatically active glucosyltransferase (GTF) with the host-derived constituents of the acquired enamel pellicle, as well as the products of GTF activity (glucans) may play a profound role on the formation and maturation of the dental plaque. GTF adsorbs preferably to salivary-coated hydroxyapatite and expresses enhanced glucan forming activity. Studies from our laboratory have also demonstrated that surface (salivary-coated hydroxyapatite) bound GTF exhibits catalytic activity over a broader range of pH (4.5-7.5) and temperatures when compared to enzyme in solution. Further, glucans formed in situ remain tightly associated with the salivary coated hydroxyapatite surface and markedly enhance the adsorption of the cariogenic streptococci S. mutans and S. sobrinus. To gain insight into the nature of the changes observed for surface-bound GTF activity, we will determine kinetic parameters (Vmax and Km) of surface-bound GFT. Second, we will identify the salivary components which influence the binding and enzymatic activity of surface (salivary-coated hydroxyapatite) bound GTF. Third, the glucans formed in situ will be characterized with regard to their structure, size and solubility. Last, the influence f in situ formed glucans on the adherence of S. mutans to pellicles pre-colonized with Actinomyces viscosus and Streptococcus sanguis will be determined. Collectively, these studies will provide considerable insight into the role played by glucans formed at the tooth surface in modulating plaque formation and development.